Implication of the NorB Efflux Pump in the Adaptation of Staphylococcus aureus to Growth at Acid pH and in Resistance to Moxifloxacin

Truong-Bolduc, Que Chi; Bolduc, Gilles R.; Okumura, Ryo; Celino, Brian; Bevis, Jennifer; Liao, Chun-Hsing; Hooper, David C.

doi:10.1128/aac.00289-11

Cited by 40 publications

(40 citation statements)

References 28 publications

(53 reference statements)

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“…Other conditions found in abscesses, such as oxidative stress and low pH, did not affect in vitro expression of opp1 or norD, but low pH has been shown to increase the expression of norB (31). Because of their upregulation in response to iron, opp1 and norD could be directly involved in iron acquisition or metabolism.…”

Section: Discussionmentioning

confidence: 99%

Staphylococcus aureus NorD, a Putative Efflux Pump Coregulated with the Opp1 Oligopeptide Permease, Contributes Selectively to Fitness In Vivo

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et al. 2012

J Bacteriol

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c Staphylococcus aureus readily infects humans, causing infections from mild superficial skin infections to lethal bacteremia and endocarditis. Transporters produced by S. aureus allow the pathogen to adapt to a variety of settings, including survival at sites of infection and in the presence of antibiotics. The native functions of many transporters are unknown, but their potential dual contribution to fitness and antimicrobial resistance highlights their importance in staphylococcal infections. Here, we show that S. aureus NorD, a newly recognized efflux pump of the major facilitator superfamily, contributes to fitness in a murine subcutaneous abscess model. In community-associated methicillin-resistant S. aureus (CA-MRSA) strain MW2, norD was selectively upregulated 36-fold at the infection site relative to growth in vitro, and the norD mutant demonstrated significant fitness impairment in abscesses, with fitness 20-to 40-fold lower than that of the parent MW2 strain. Plasmid-encoded NorD could complement the fitness defect of the MW2 norD mutant. Chromosomal norD expression is polycistronic with the upstream oligopeptide permease genes (opp1ABCDF), which encode an ABC oligopeptide transporter. Both norD and opp1 were upregulated in abscesses and iron-restricted culture medium and negatively regulated by Fur, but only NorD contributed to fitness in the murine abscess model. Staphylococcus aureus is a versatile pathogen that causes a variety of diseases from food poisoning, skin infections, and abscesses to lethal bacteremia and endocarditis (21). Its adaptability is facilitated by a range of virulence factors and by factors that contribute to its survival and fitness in multiple environments within the host (2). Among the contributors to S. aureus fitness are a range of transmembrane transporters that can mediate uptake of nutrients or export of metabolites and toxic substances, including in some cases export of antimicrobial agents causing antimicrobial resistance (5,9,15,16,26,28).We found previously that several staphylococcal efflux pumps were selectively overexpressed within the milieu of experimental subcutaneous abscesses and that these pumps not only contributed to antimicrobial resistance when overexpressed in vitro but also contributed to bacterial survival within the abscess in the absence of antimicrobial agents (12). Both NorB and Tet38, members of the major facilitator superfamily (MFS) of secondary transporters encoded on the S. aureus chromosome, contributed selectively to fitness in the abscess environment and conferred low-level resistance to fluoroquinolones and tetracycline, respectively.In order to identify other transporters that might also be important for bacterial survival in this environment, we evaluated the MFS transporter NorD. Like norB and tet38, norD expression was selectively upregulated in abscesses. Herein, we present data indicating that NorD contributes substantially to S. aureus fitness in an abscess infection model, and we identified a low-iron environment as a potential ...

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Section: Discussionmentioning

confidence: 99%

Staphylococcus aureus NorD, a Putative Efflux Pump Coregulated with the Opp1 Oligopeptide Permease, Contributes Selectively to Fitness In Vivo

Ding

Lee

et al. 2012

J Bacteriol

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“…Moreover, the authors of that study suggested that NorA, which confers low-level resistance to several antibiotics, may also participate in the secretion of siderophores, which might be its natural function. As another example, in S. aureus, resistance to moxi-floxacin can be acquired by the upregulation of NorB during growth at a low pH (244). This regulation is exerted via the negative regulator MgrA, which must be in a phosphorylated form to be active in preventing norB transcription.…”

Section: Adaptation Mediated By Efflux Pumpsmentioning

confidence: 99%

Adaptive and Mutational Resistance: Role of Porins and Efflux Pumps in Drug Resistance

2012

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SUMMARY The substantial use of antibiotics in the clinic, combined with a dearth of new antibiotic classes, has led to a gradual increase in the resistance of bacterial pathogens to these compounds. Among the various mechanisms by which bacteria endure the action of antibiotics, those affecting influx and efflux are of particular importance, as they limit the interaction of the drug with its intracellular targets and, consequently, its deleterious effects on the cell. This review evaluates the impact of porins and efflux pumps on two major types of resistance, namely, mutational and adaptive types of resistance, both of which are regarded as key phenomena in the global rise of antibiotic resistance among pathogenic microorganisms. In particular, we explain how adaptive and mutational events can dramatically influence the outcome of antibiotic therapy by altering the mechanisms of influx and efflux of antibiotics. The identification of porins and pumps as major resistance markers has opened new possibilities for the development of novel therapeutic strategies directed specifically against these mechanisms.

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“…Various studies have demonstrated that environmental stresses, such as a low oxygen level or a high carbon dioxide level at a neutral pH, are necessary for the production of exotoxins, including the synthesis of toxic shock syndrome toxin 1 (TSST-1) (18,30). Recently, we demonstrated that acid pH influences the expression of the MgrA transcriptional regulator, modulating its state of phosphorylation through changes in the Ser/Thr kinase PknB (22). S. aureus is facultatively anaerobic and able to grow under reduced-oxygen conditions by switching its aerobic respiratory mechanism to fermentation or nitrate respiration, with lactate or nitrate (NO 3 Ϫ ) and nitrite (NO 2 Ϫ ) as terminal electron acceptors under anaerobic conditions (9,19).…”

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Reduced Aeration Affects the Expression of the NorB Efflux Pump of Staphylococcus aureus by Posttranslational Modification of MgrA

et al. 2012

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We previously showed that at acid pH, the transcription of norB, encoding the NorB efflux pump, increases due to a reduction in the phosphorylation level of MgrA, which in turn leads to a reduction in bacterial killing by moxifloxacin, a substrate of the NorB efflux pump. In this study, we demonstrated that reduced oxygen levels did not affect the transcript levels of mgrA but modified the dimerization of the MgrA protein, which remained mostly in its monomeric form. Under reduced aeration, we also observed a 21.7-fold increase in the norB transcript levels after 60 min of growth that contributed to a 4-fold increase in the MICs of moxifloxacin and sparfloxacin for Staphylococcus aureus RN6390. The relative proportions of MgrA in monomeric and dimeric forms were altered by treatment with H 2 O 2 , but incubation of purified MgrA with extracts of cells grown under reduced but not normal aeration prevented MgrA from being converted to its dimeric DNA-binding form. This modification was associated with cleavage of a fragment of the dimerization domain of MgrA without change in MgrA phosphorylation and an increase in transcript levels of genes encoding serine proteases in cells incubated at reduced aeration. Taken together, these data suggest that modification of MgrA by proteases underlies the reversal of its repression of norB and increased resistance to NorB substrates in response to reduced-aeration conditions, illustrating a third mechanism of posttranslational modification, in addition to oxidation and phosphorylation, that modulates the regulatory activities of MgrA.

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Implication of the NorB Efflux Pump in the Adaptation of Staphylococcus aureus to Growth at Acid pH and in Resistance to Moxifloxacin

Cited by 40 publications

References 28 publications

Staphylococcus aureus NorD, a Putative Efflux Pump Coregulated with the Opp1 Oligopeptide Permease, Contributes Selectively to Fitness In Vivo

Staphylococcus aureus NorD, a Putative Efflux Pump Coregulated with the Opp1 Oligopeptide Permease, Contributes Selectively to Fitness In Vivo

Adaptive and Mutational Resistance: Role of Porins and Efflux Pumps in Drug Resistance

Reduced Aeration Affects the Expression of the NorB Efflux Pump of Staphylococcus aureus by Posttranslational Modification of MgrA

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